1. Field of the Invention
The present invention relates to a non-isolated switching regulator.
2. Description of Related Art
As disclosed in Japanese Patent Application Laid-Open No. 2002-44939, a switching regulator, which includes two switching elements (PMOS transistor and NMOS transistor) connected to each other in a push-pull manner for applying alternating current to an inductor is known as a conventional switching regulator. This kind of switching regulator preferably has a function that prevents the current passing through the inductor from flowing in reverse to the NMOS transistor, particularly when the output of the switching regulator has a light load. As a result of this function, power loss generated by the reverse flow of current due to the ON resistance of the NMOS, can be reduced. One technique to prevent current passing through the inductor from flowing reverse includes monitoring a potential of a terminal of the NMOS transistor and turning off the NMOS transistor when the monitored potential is lower than the ground potential.
In general, switching regulators are designed such that the two switching elements (PMOS transistor and NMOS transistor) connected to each other in a push-pull manner have extremely small ON resistance, in order to improve efficiency. Therefore, the potential generated at the terminal of the NMOS transistor connected to the inductor (hereinafter, the “inductor side terminal of the NMOS transistor”), i.e., generated by the ON resistance of the NMOS transistor, is extremely close to the ground potential. Thus, when the potential at the inductor side terminal of the NMOS transistor is compared with the ground potential by a comparator, results of the comparison are significantly affected by the offset variation of the comparator. Accordingly, the problem has existed that the timing when the current passing through the inductor flows in reverse cannot be detected precisely. In view of the above, there has been a need for a switching regulator that can reliably prevent the current passing through the inductor from flowing in reverse to the switching element.